This invention relates to an electro-optical hybrid wiring board suitable for use to handle both optical and electrical signals, and a method for making same.
There have evolved examples in which a portion of an apparatus is constructed of optical circuits for the purpose of increasing the response speed of the apparatus, eliminating the interference between the circuits, or the like.
An example of the construction of the prior art electro-optical hybrid apparatus is illustrated in FIG. 1 in which the reference numeral 11 indicates a mother board while 12 are daughter boards mounted to the major surface of the mother board 11 in an orientation perpendicular to the plane of the mother board. The daughter boards 12 are electrically connected with the mother board 11 by means of electrical connectors 13 mounted to the major surface of the mother board 11.
On the other hand, the interconnections between the daughter boards 12 for optical signals are separately established by optical communication modules 15 and optical fibers 16.
In the conventional electro-optical hybrid apparatus, while the electrical interconnections between the daughter boards are collectively effected by the electrical connectors 13 and mother board 11, optical signal interconnections must be made separately for each route by means of the optical communication modules 15 and optical fibers 16. The optical communication modules 15 and optical fibers 16 are configured to be detachably connected together by optical connectors 17. However, for a large scale apparatus such as an IC tester, a tremendous amount of labor is required for the connecting and disconnecting operations because of the great number of optical signal paths which may amount to as many as several thousands. Although there are available optical connectors capable of connecting and disconnecting a plurality of optical fibers at one time, such configuration of connection could not cope with an enormous number of optical signal paths as many as several thousands. In addition, misconnections are likely to occur, and undesirably much labor is required for the assembly.
Wim Delbare and Louis Vandam deals with the configuration of connection for numerous glass optical fibers embedded in the surface layer of an electro-optical board in their "ELECTRO-OPTICAL BOARD TECHNOLOGY BASED ON DISCRETE WIRING", Proc. International Electronic Packaging Conf., pp. 604-618, 1991. According to this connecting method, a supporting glass fiber (or copper wire) is laid on a wiring board to extend in a straight line and a plurality of glass optical fibers are arrayed so as to cross perpendicularly over the supporting glass fiber whereby the optical fibers will have bent portions protruding upwardly. These fibers are then embedded in a filler layer to form an electro-optical board (daughter board ). The upper surface of the filler layer is shaved to expose the raised bent portions of the fibers, which raised portions are ground to form optical coupling faces, against which optical couplers disposed in a mother board are opposed to optically connect the optical fibers of the electro-optical board with those of the wiring board (mother board) oriented perpendicularly to the electro-optical board. This connecting approach allows for collectively interconnecting numerous optical fibers between a mother board and daughter boards, but is involved with difficulties in grinding many arrayed bent portions of optical fibers by the same depth to the cores of the optical fibers and consequently suffers from the drawback of significant variation in the optical coupling characteristics.